The Why Files The Why Files --

Microbial bliss: Meet the bugs in your gut!

Holy Cow: Beneficial bacteria on the march!

To tame global warming, some agricultural scientists are trying to de-gas the cow, whose rumen harbors gazillions of microbes that convert cellulose into nutrients for the cow – and also make plenty of methane. And because a ton of methane warms the planet as much as 21 tons of carbon dioxide, cattle are responsible for most of agriculture’s global warming impact.

A flat brown dusty feedlot crossed by two roads contains white, black and brown cattle
A 2006 report from the United Nations said that the livestock industry's contribution to human-caused climate change (as measured in CO2 equivalent) was a billowing 18 percent. That's more than all global transport! The 47,000 head of cattle in this Texas feedlot pump out about 16.5 million liters of methane per day.

According to the United Nations, agriculture is warming the globe more than transportation – no small feat.

We’ve heard of nascent efforts to cut per-cow methane emissions by 25 percent. That’s sensible – at this rate, both we and our cows will cook like chicken-fried steak in the gathering storm called global warming.

Although we failed to find a scientist willing to explain how to modulate bovine production of greenhouse gases, those methanic headlines got us to thinking about the microbes in our own guts.

These critters, mainly bacteria, vastly outnumber the cells in our bodies, and we are utterly dependent on them. Bacteria make vitamin K, essential for clotting blood. As they do in cows, bacteria play an essential role converting our food into usable chemicals. And bacteria form a complex barrier against invading pathogenic microbes.

When our microbes go haywire (or AWOL), we get sick, and we are not just talking a sour stomach.

Historically, medicine’s response to bacteria is to waste them with antibiotics, but we have now entered a period of counter-revolution. In some cases, deliberately consuming bacteria (in foods or supplements) can be more healthful than trying to kill bacteria. In other cases, the treatment strategy involves killing some bugs and eating others.

The science is complex, evolving and incomplete. A survey of existing research published in 2008 (see #1 in the bibliography) found that probiotics seem to help in many conditions, especially those related to the intestines (very few microbes can survive in the highly acidic stomach):

Diseases of the intestines: Studies have shown moderate to good effect for treating or preventing inflammatory bowel disease, and also for a milder condition called irritable bowel syndrome.

Intestinal infection: One of the best-studied benefits of probiotics is preventing diarrhea caused by bacteria that occupy the gastrointestinal (GI) tract after it has been scoured clean of bacteria by antibiotics. Perhaps the best example concerns infections with Clostridium difficile (C. diff), a nasty spore-forming bacterium that is now sickening people both inside and outside hospitals.

Eczema: Probiotics can help prevent and treat this common skin condition, which seems to be rooted in an immune problem.

Boosting immune function: Bacteria in the intestines are detected by the immune system, and, as we’ll see later, scientists have recently shown that probiotics substantially reduced respiratory illnesses in a group of athletes.

The actual range of probiotic investigations is much wider; researchers are at early stages of exploring, for example, whether probiotics may help with other conditions, such as obesity.

Not just for quacks

As we began talking with people doing research on probiotics, we had to ask if their long promotion by alternative healers had hindered the study of bugs in the gut. What hard-nosed, lab-bound PhD would want to be associated with acupuncturists, nutritional healers and massage therapists, who have touted the benefits of eating yogurt (which can contain strains of lactobacillus, a beneficial intestinal bacteria) and other sources of probiotics?

 Ingredients listed on a yogurt cup include bifidum cultures, L. acidophilus, and L. bulgaricus
Many types of yogurt contain live cultures of bacteria that are thought to be probiotic. But experts say it helps to know the exact strain, not just the species.

Probiotics are leaping into the scientific mainstream, says Gary Huffnagle, professor of internal medicine and microbiology at the University of Michigan Health System and author of a recent popular book on beneficial bugs (see #2 in the bibliography). “You can see an absolute explosion in the number of research publications on probiotics. There have been amazing observations of how important the bacteria in our body are for health.”

A white woman’s palm holds a large white tablet and a smaller capsule against a black background
Some people take probiotics to counter the effects of antibiotics, but it's probably better to wait until you have quit the antibiotics before starting to gobble the probiotics.
Photo: lu_lu

A springboard for the growing interest, Huffnagle says, was a discovery by Jeffrey Gordon of Washington University, who found that bacteria “can talk to the epithelial cells that line the GI tract, which can turn on different genes depending on who is living nearby.”

A mutually beneficial relationship – with bugs?

Because the payoffs from this relationship flow both directions, Huffnagle says many gut bacteria “form a true symbiosis, a mutualistic association between bacteria and cells in our body.”

As a result, Huffnagle says, research from the 1950s and ‘60s, about the role of intestinal microbes in health, “is being reexamined with our new understanding of biology and all this incredible new technology” used in biology labs.

Which is not to say these studies are easy. To really understand the effect of adding bacteria to the GI tract, we need to understand gut bacteria -- a big job. We have 10 times as many gut bugs as we do cells in our bodies. At least 400 bacterial species live in the gut, each of which may comprise a hideously complicated web of sub-strains.

The exact composition of microbes in a specific person (host), at a given time reflects interactions among the many strains of gut microbes, and other factors:

Host genetics;

Host health, including infections, use of antibiotics and immune health;

History of exposure to microbes (the first to colonize the gut can obtain a lifelong advantage); and

Host diet. Some foods contain probiotics, others contain “prebiotic” compounds that foster the growth of beneficial bacteria.

“Probiotic” means “for life,” which the World Health Organization defines as “Live microorganisms which when administered in adequate amounts confer a health benefit on the host.”

Nobody argues against gobbling yogurt, but if you are going to buy probiotic supplements, it would help if somebody had proven their benefits!

Let’s check out some of the better studied benefits of probiotics.


Terry Devitt, editor; Nathan Hebert, project assistant; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

©2022, University of Wisconsin, Board of Regents.